Strength and softness are important attributes in consumer paper products such as bathroom tissue, towels, and napkins. These two attributes are strongly influenced by the sheet structure of a paper product. Further, the types of fiber employed in the sheet are important factors in determining the strength and softness of products made from such fibers.
Strength and softness typically are inversely related. That is, the stronger a given sheet appears, the less soft that sheet will be. Likewise, a softer sheet is usually not as strong. Thus, it is a constant endeavor in the industry to produce a sheet having a strength which is at least as great as conventional prior art sheets, but with improved softness. Also, a sheet which is at least as soft as conventional sheets, but with improved strength, is desirable.
It is common in the manufacture of paper products to provide two furnishes or slurries of fiber. Sometimes, a two-furnish system is used in which the first furnish is comprised of eucalyptus wood fibers, and the second furnish is made of higher grade wood fibers, such as fibers from Northern softwood and the like. In general, more desirable fibers with better softness are provided in outer layers of paper productsxe2x80x94which routinely contact the skin of consumers. The inner layers of paper products typically comprise coarse fibers which are less desirable in their properties of softness, absorbency, or strength. Thus, in this way the desirable properties of the paper products can be maximized at a minimal cost in raw materials.
The use of two separate slurries of furnish is an expensive process, and requires a relatively large amount of processing equipment. It is more difficult to rely on the supply of two different materials in the manufacture of one product. Further, it is more complex to produce a product when more than one type of raw fiber material is used in a manufacturing process.
Fractionation is the process by which cellulosic fibers are separated according to their properties. U.S. Pat. No. 6,024,834 to Horton, Jr. is directed to a process of separating by fractionation cellulosic fibers that exhibit desired properties such as fiber length and fiber coarseness values. The process has been found to produce cellulosic fibers that are more homogeneous in their properties as compared to the starting mixtures of cellulose fibers. Paper products may be prepared from fractionated cellulosic fibers for use in absorbent disposable products.
Fines and short fibers are the least desirable fibers in most fiber slurries. In the past, such fines comprised short portions of cellulosic material which do not appreciably contribute to softness. Further, such fines are too small to remain on a wire former in the papermaking process, and often fall through the wire mesh of the wire former with the water when a paper slurry is applied on the twin wire former in the early stages of paper or paper products manufacture. Further, fines comprise cellulosic particles that undesirably absorb a large amount of the treatment chemicals that are used in the headbox at the early stages of slurry formation. Thus, fines are often simply washed from the system, and may not contribute in any meaningful way to the final paper product. In fact, such fines may undesirably absorb process chemicals which otherwise could be applied to the longer fibers which in fact do become part of a paper product. In this way, fines waste processing chemicals by carrying such chemicals out of the processing system.
It would be desirable to provide a process and method which can be used to supply a single furnish of cellulose, and then produce a high quality paper product. Further, a paper products and process of making such a product in which fines, short fibers, and/or fibrils can contribute in a positive manner to the final paper product, rather than acting in a negative manner as a chemical xe2x80x9cspongexe2x80x9d or waste material, would be very desirable. A method that is capable of separating a single furnish into multiple components would be valuable. Further, a process that is able to employ fines, short fibers, and long fibers in a way that provides a paper product with desirable strength and softness would be advantageous.
The present invention addresses the needs described above by providing a method of making an absorbent paper product using fines or short fibers in a new and more advantageous manner. Furthermore, a product incorporating such materials is provided by way of this invention.
The invention provides a process of making an absorbent structure comprising several steps. In one step, a cellulosic fiber mixture is provided for fractionating the first cellulosic fiber mixture into a second fiber mixture having relatively short fibers and fines, and a third fiber mixture having relatively long fibers. Then, the third fiber mixture is treated with chemical agents to soften the fibers. In a next step, the third fiber mixture is provided to a paper machine, thereby forming a paper sheet from said third fiber mixture on a wire former. Then, the step of adding the second fiber mixture to the upper surface of the paper sheet is provided.
In one embodiment of the invention, the chemical agents comprise surfactants. Further, a process is disclosed in which the chemical agents comprise enzymes. The process also may include using chemical agents that comprise debonders. The process also may provide for treatment with chemical agents that comprise surfactants and enzymes. The process also may be utilized in which the first cellulosic fiber mixture comprises recycled newspapers. The process is further provided in which a single furnish is used as a source of the cellulosic fibers.
A process is provided that includes the additional step of disposing of fines which are not incorporated into the paper sheet. A method of making sanitary paper products from newspapers containing coarse cellulose fibers is also provided. The method comprises pulping the newspapers in water with agitation to produce a pulp slurry furnish. Then, the pulp slurry furnish is fractionated into a slurry of short fibers and fines, and a slurry of long fibers is produced. The slurry of long fibers is then treated with chemical agents to soften the fibers. In an additional step, a slurry of long fibers is provided to a paper machine, thereby forming a paper sheet from said third fiber mixture on a wire former. In another step, one adds the slurry of short fibers and fines to the upper surface of the paper sheet.
In one aspect of the invention, an absorbent paper product is made by the process comprising providing a first cellulosic fiber mixture, and then fractionating the first cellulosic fiber mixture into a second fiber mixture having relatively short fibers and fines, and a third fiber mixture having relatively long fibers. Then, another step of treating the third fiber mixture with chemical agents to soften the fibers is provided. In a further step, one provides the third fiber mixture to a paper machine, thereby forming a first paper sheet from said third fiber mixture on a wire former. The first paper sheet has an upper and lower surface. The next step includes adding the second fiber mixture to the upper surface of the first paper sheet. Then, a step of drying said first paper sheet is provided. In a further step, the first paper sheet is combined with at least one additional paper sheet to form a multi-ply paper product.
In another aspect of the invention, a paper product is provided in which the multi-ply product comprises at least two layers. The paper product may comprise a tissue, towel, or napkin. The paper products may comprise one ply having two layers. The paper products also may be employed with one ply having three layers, the three layers comprising a middle layer and two outer layers. In some embodiments, the paper products includes a first paper sheet having short fibers and fines comprising the middle layer.
Paper products comprising more than one ply are shown in some aspects of the invention, wherein each ply comprises a plurality of layers, the paper products having at least one inner layer comprising short fibers and fines. In general, the inner layer is formed by providing a first cellulosic fiber mixture and then fractionating the first cellulosic fiber mixture into a second fiber mixture having relatively short fibers and fines, and a third fiber mixture having relatively long fibers.
In a further embodiment of the invention, one may treat the third fiber mixture with chemical agents to soften the fibers. In another aspect of the invention, one may provide the third fiber mixture to a paper machine, thereby forming a first paper sheet from the third fiber mixture on a wire former. The first paper sheet generally includes an upper and lower surface. In one other aspect of the invention, the second fiber mixture is added to the upper surface of the first paper sheet to form an inner layer. Then, one may combine the inner layer with other layers to form a paper product.
The paper products may comprises two plies. In some embodiments, paper products are disclosed in which the first cellulosic fiber mixture is recycled newsprint. In one aspect of the invention, the outer layers contain fibers of longer average length than the inner layers. Paper products are disclosed in which two plies are employed, each ply having two layers, wherein the chemical agent employed is a surfactant, the paper products having an increased Handfeel value.
In another aspect of the invention, the paper products are shown in which the Handfeel value at a Geometric Tensile Strength/Basis Weight of about 9 is at least about 70 or greater.
In one aspect of the invention, paper products are provided which comprise more than one ply, wherein each ply of the paper products includes a plurality of layers. The paper products also have at least one inner layer comprising short fibers and fines, the inner layer being formed in part by fractionating a single furnish of cellulose fibers into separate slurries, the respective slurries being characterized by fibers of different length, wherein a first slurry is comprised of fines. The first slurry of fines is applied upon the upper surface of a paper sheet in a papermaking machine. The paper sheet is comprised in part of relatively long fibers, and the fines adhere to the long fibers of the paper sheet. The paper sheet further is combined with other paper sheets to form paper products.